Publication Date: 2010-May-10
The IP.com Prior Art Database
This invention relates to a cup. In particular, the invention relates to a cup for implantation into a bone to form part of a prosthetic joint. An exemplary embodiment of the present invention relates to an acetabular cup for implantation into a cavity prepared in the acetabulum of a patient.
This invention relates to a cup. In particular, the invention relates to a cup for implantation into a bone to form part of a prosthetic joint. An exemplary embodiment of the present invention relates to an acetabular cup for implantation into a cavity prepared in the
acetabulum of a patient.
The acetabular cup component of a hip joint prosthesis typically comprises a part-spherical shell which can be implanted in the patient's acetabulum. Generally the shell is formed from a metallic material. A liner component may be fitted to the shell. Alternatively, there
may be no liner component such that articulating contact with the convex femoral head component is metal-on-metal.
It is known to provide an acetabular cup having cut away portions. For instance, US-2910978 discloses an acetabular cup which has a notch formed in it. Figure 1
illustrates an acetabular cup 2 of the sort disclosed by US-2910978. The notch 4 has a rounded portion 6 towards the pole of the component, and a narrower neck portion 8 which extends from the rounded portion 6 to the rim 10 of the cup 2. The rounded portion 6 is generally positioned about the central axis of the cup 2.
The notch 4 allows fat pad tissue in the acetabular fossa to be preserved when the acetabulum is prepared to receive the prosthesis component. Thus, such an acetabular cup may be referred to as a tissue sparing cup (TSC). Preservation of the fat pad tissue can promote lubrication of the joint during articulation. The rounded portion 6 of the notch 4 forms an opening which permits the passage of synovial fluid and other lubricating
secretions to the bearing surfaces. An increase in lubrication within a prosthetic joint can reduce wear of the prosthetic components.
Commercially available tissue sparing cups, similar to the cup disclosed in US-2910978, include a cut out which extends through the entire wall of the cup. Typically, such cups
are of relatively large diameter and allow for metal-on-metal articulating contact with the convex bearing surface of the femoral component.
However, tissue sparing cups suffer from a number of disadvantages. During press fitting into the prepared bone cavity the cup may be deformed due to the reduction in strength inherent in removing part of the contact portion of the cup, and especially due to removing part of the rim. Deformation of the cup is particular undesirable for cups providing metal-
on-metal contact with the femoral head due to the small clearance required for metal-on- metal articulating contact.
The problems associated with this deformation may be addressed by increasing the clearance between the articulating surfaces. However, this can lead to increased wear and
also results in a looser assembled joint. Alternatively, the rigidity of the cup can be increased. However, increasing cup rigidity typically increases the overall size and weight of the cup and may require more bone to be removed to...